Ng admitted to possessing 11 bras in his flat at Bishan Street 22, which the police suspect were stolen. (Bishan Street 22 is not an address.It is the name of the street.)

The above is a sentence from a local newspaper.

Is 'at' the correct preposition?

Thanks.

I'd go with in or on depending on whether you're writing for a British or a US audience respectively. I couldn't say for other brands of English. I'd only use ]at if it were an address.

On is the correct preposition.